1. Field of the Invention
This invention relates generally to liquid transfer systems and more particularly provides a pneumatically operated liquid transfer valve having a linearly movable valve element carrying measuring passageways oriented to effect gravity induced drainage.
2. Description of the Prior Art
In the U.S. Pat. No. 3,549,994, there was provided a structure in which a sample of blood is driven into a fluid system in which it is accurately diluted with a suitable diluent and divided into two samples for red and white blood cell determination. The red sample for red cell determination is counted and sized utilizing a COULTER scanning device and is discharged, while at the same time the other is lysed to break up the red cells and subjected to another COULTER electronic scanning device for a white cell count with the simultaneous examination of the sample for hemoglobin determination and discharge. Processing is automatic and continuous for samples drawn into the apparatus at intervals exceeding at least a certain minimum time duration. The structure therein disclosed included means for combining the data automatically to ascertain certain of the parameters which are susceptible of derivation for determinations made, and producing data corresponding to all of the parameters both determined and derived from the apparatus. These parameters were blood counts, sizes, percentages, and the like, accepted in the medical arts as aids for diagnosis, treatment, and research. The structure therein disclosed utilized vessels, valves, and connecting conduits for the intermixing and/or diluting of fluids primarily for the purpose of making measurements and tests on such fluids. Of course, it should be appreciated that such description is somewhat general and while primarily utilized with an automatic instrument such as disclosed in the above-identified patent and employs the particle analyzing apparatus of the type disclosed in U.S. Pat. No. 2,656,508, it is capable of many uses. In medicine, biology, chemistry, and allied fields, research as well as routine testing required the use of apparatus which can produce fluid mixtures of specific concentrations accurately and automatically and particularly, can feed known quantities of fluids to a selected one of a plurality of locations.
In the apparatus referred to in U.S. Pat. No. 3,549,994, samples of whole blood were introduced one every fifteen seconds. The apparatus performs the requisite dilutions, tests, and computations needed for obtaining blood counts of white and red cells, a hematocrit determination, a hemoglobin measurement, and so on. Accordingly, such automatic instrument is required quickly and accurately to prepare the necessary sample suspensions of predetermined concentration for transfer to the testing apparatus of the instrument. Liquids must be pumped, transferred and moved between vessels and it is with such type of liquid transfer apparatus that this invention is concerned.
One type of the liquid transfer valve structure has been disclosed in U.S. Pat. No. 3,567,390 and that particularly consisted of a central element and a pair of outer elements engaged against opposite faces o the central element to sandwich same therebetween. The central element is movable relative to the other element between first and second positions. At least one measuring conduit is formed in the central element and at least a pair of ports are provided in each outer element. Each of the ports in one of the outer elements aligns with a port carried by other outer element so that two fluid paths are defined. The central member is indexed to a first position to align one measuring conduit with one of said fluid paths for reception in that one conduit of a portion of the fluid sample. The central element then is moved to a second position. By virtue of such movement, a quantity of the sample is segmented by means measuring conduit and deposited in the other fluid path for combining with a diluent introduced therein so as to deliver a precise dilution.
In the various fluid transfer valve constructions disclosed in the aforesaid patents, the segmenting passageways were oriented horizontally and further included associated therewith plural drive components that required maintenance of very close tolerances in manufacture. Failure to meet those close tolerances would result in either inaccurate alignment, movement, and the like, effecting the accurate measuring and transfer of the liquid. For example, when a leak formed in the valve, air may be drawn in with the sample being measured due to the vacuum associated with the drawing of the liquid sample. When to the extent that such air leaked replaces the volume that should be occupied by the liquid sample, the dilution ratio sought cannot be met and error results.
It would be desirable to permit such entrapped air to leave the segmented portion prior to the operation of the central element effecting such segmentation. If this is accomplished, then not only do proper dilution ratios occur but, much of the close tolerances mandatory in earlier valves may be relaxed since air leaking into the valve does not create erroneous measurements. Likewise, an arrangement that enables drainage under gravitational influence improves clearance of the valve passageways.
The trademark COULTER is a registered trademark, Registration No. 995,825, owned by Coulter Electronics, Inc. of Hialeah, Florida.